The discussion throughout this specification comes about due to the realisation of the inventors and/or the identification of certain prior art problems by the inventors.
The applicants are aware of a number of transponder systems that provide two dimensional, limited three dimensional or full three dimensional interrogator capabilities. These systems utilise a multiplicity of interrogator coils operating in different coordinate axis, to achieve the resultant two or three dimensional operation.
One example of an interrogator which produces a relatively uniform field in three dimensions is disclosed in U.S. Pat. No. 5,258,766 and international application PCT/AU95/00436. This form of interrogator is known as a Tunnel Reader Programmer (TRP). While a TRP has three dimensional interrogation properties, the inventors have realised that this technology is suitable for applications where the RFID transponders are moved in and out of the TRP, usually on a conveyor or similar. There is still a need to provide an interrogator which is adapted to operate on a relatively flat surface such as a shelf, storage system, table or wall. For these applications relatively flat planar antenna coils may be used.
The inventors have also realised that relatively flat planar antenna coils produce fields in only one direction at any point relative to the coil and do not have a three dimensional interrogation capability.
The inventors have further realised that when items are stored, for example, on shelving, storage systems, draws or other means of storage, the orientation of the item, and consequently, the orientation of the tag associated with the item cannot be guaranteed to be in alignment with the direction required for interrogation, especially by a flat planar antenna coil. Thus, if RFID and remote powering is used in applications where orientation of items to be identified cannot be guaranteed, such as shelving and storage systems, medical device tracking, document tracking, luggage identification, gaming tokens, by way of example only, the above identified problem can lead to items being missed, that is, not correctly identified.
WO2007/030861 discloses an antenna design and method of operation which enables a 3 dimensional interrogation field to be created from a flat planar antenna. In essence, the disclosure of WO2007030861 provides for a series of parallel spaced conductors through which currents are sequentially switched in order to produce both tangential and normal magnetic field components. The spatial relationship of the sequentially switched currents is chosen to ensure that at different times a tangential and a normal magnetic field components are produced at the same location. The conductors are preferably arranged in a planar fashion and the tangential and normal magnetic fields are produced above (or below) the planar surface. A single layer of parallel spaced conductors provides for two dimensional operations. Adding a second parallel layer of orthogonally oriented parallel spaced conductors provides three dimensional operations where currents are sequentially switched in both layers.
FIG. 1 illustrates, in schematic form, a conventional single coil of rectangular form through which a current flows. The resulting magnetic field directions are shown and related to the X, Y and Z coordinate directions. At different regions above (or below) the coil, the magnetic field has a unique direction which is variously in the X, the Y or the Z directions, or some combination of these directions in transition regions. FIG. 2 illustrates these regions.
FIG. 3 shows an array of coils and illustrates how, when appropriately switched, a field in the X, Y and Z directions is produced as described in WO2007/030861. In this regard, by suitably overlapping generally rectangular coils and then sequentially switching each coil so that only one coil is active at any time, at any point above (or below) the overlapped coils, a field in the X direction, the Y direction and the Z direction may be produced at some time. In order to suitably switch the coils as shown in FIG. 3, the signal from an RFID reader must be controlled by a MUX circuit which directs the RFID reader signal to each coil in the array in a sequentially manner. In addition to the MUX, special circuits in each coil are required to tune the coils and ameliorate the effects of coupling (both capacitive and inductive) between coils which can lead to the generation of parasitic currents in the inactive coils. These parasitic currents may cause, amongst other things, distortion of the active coil's magnetic field, changes in the active coil's tuning, increase of the active coil's losses and a reduction of the RFID current in the active coil. These parasitic currents are considered undesirable.
The inventors are aware that the circuits described in application WO2009/149506 that control the switching of the coils in the antenna array and ameliorate the effect of stray coupling, also may add to the complexity and cost of the antenna array. Where a relatively large array area is required, it is considered that both the cost and complexity of the array may become very high. A relatively high cost of a relatively large area antenna array is considered an impediment which may prevent the implementation of RFID in various applications.
Australian Patent Application 2013201425 describes how an antenna is shifted (displaced or moved) in at least one, or in any combination of the x, y and/or z directions in order to create the effect of interrogation by a relatively large antenna array in 1, 2 and/or 3 dimensions. The invention provides for a method of creating an arbitrarily large array that can read in 1, 2 or 3 dimensions by shifting an antenna or small antenna array in one or more plane(s) to create a large “virtual” array. The process of sequentially switching coils (as shown in the prior art) is replaced with at least a single coil, or smaller coil array, which is shifted to a series of positions within an interrogation area, where at each position, interrogation is undertaken or activated in order to mimic the process of sequentially switching an (otherwise) larger coil array. The invention shown in Australian Patent Application 2013201425 is advantageously suited to relatively large fixed shelving and storage installations such as are shown in FIG. 7 and FIG. 8 of Australian Patent Application 2013201425 where there is a need to create an antenna array that can read in 1, 2 or 3 dimensions over a relatively large area at a reduced cost. Such an antenna would be considered highly advantageous and allow the wide scale adoption of RFID in applications where the high implementation cost has previously prevented the adoption of RFID.
There are however shelving applications where an RFID enabled cabinet such as shown in FIG. 34 of WO2007030861 may be advantageous to use rather than a relatively large fixed RFID shelving installations. The RFID shelving cabinet as shown in FIG. 34 of WO2007/030861 incorporates the planar antenna array described in WO2007/030861 into some or all of its shelves. Such an RFID shelving cabinet may be advantageous, for example, because cabinets can be easily made portable by being mounted on wheels. This feature can be advantageous for example in a hospital where a cabinet with all the supplies for an operation can be wheeled into an operating theatre and the supplies used during the operation can be automatically recorded for stocktake, billing and ordering purposes. Another advantage of an RFID shelving cabinet may be, for example, that it can be fitted with lockable doors which may be used to control access for security or billing purposes.
FIG. 4 shows an example prior art RFID enabled portable cabinet 401 which is mounted on wheels 405. The portable cabinet 401 includes a number of RFID enabled shelves 403 that include RFID antennas. These are connected using RF cable 404 to a reader 402. The reader is powered and communicates with other devices through cable 406. This reader could however be powered from a local battery and/or the external communication could be by a wireless connection.
An RFID enabled cabinet would typically require a planar antenna array as described in WO2007/030861 to be incorporated into some or all of its shelves. FIG. 5 shows a section of an RFID enabled cabinet 501 with two shelves 502. Each shelf consists of an external housing 503 and an internal planar antenna array 504. The antenna array is connected to the reader (not shown) by an RF cable 505. The cost of the planar array antennas 504 is high and each cabinet may have 5 or more shelves 502 with antennas 504. The large number and high cost of these antenna arrays makes the cost of such RFID enabled cabinets high and is a serious impediment to their wide scale adoption.
One exemplary solution is to incorporate a movable antenna as described in Australian Patent Application 2013201425 into each cabinet shelf. For a typically square shelf any movable internal antenna array would need to be half the size of the shelf. The reduced cost advantage of the smaller sized internal movable array is offset somewhat by the added mechanical complexity of the translation mechanism however overall it would provide for an advantageous reduction in the cost of the RFID enabled cabinet. The cost of antennas and other mechanical mechanisms is however still a significant part of the overall cost of an RFID enabled cabinet and is a serious impediment to their wide scale adoption.
In many RFID enabled cabinet applications the identification of tagged items for stocktaking, billing or ordering purposes is not required on a real time basis and need only be done on a per use, daily or other infrequent basis. The inclusion of high cost RFID electronics into a storage cabinet where the RFID electronics is only used on an infrequent basis is thus considered expensive, inefficient and an impediment to the wide scale adoption of RFID.
There is thus a need to create an RFID enabled cabinet and/or storage system and/or method which is relatively scaleable. Such a cabinet would be considered highly advantageous and allow the wide scale adoption of RFID in applications where the high implementation cost has previously prevented the adoption of RFID.
Throughout this specification the use of the word “inventor” in singular form may be taken as reference to one (singular) inventor or more than one (plural) inventor of the present invention.
It is to be appreciated that any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the present invention. Further, the discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related art problems by the inventor. Moreover, any discussion of material such as documents, devices, acts or knowledge in this specification is included to explain the context of the invention in terms of the inventor's knowledge and experience and, accordingly, any such discussion should not be taken as an admission that any of the material forms part of the prior art base or the common general knowledge in the relevant art in Australia, or elsewhere, on or before the priority date of the disclosure and claims herein.